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Horn Sharks. Heterodontidae species.
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page are copyright protected: © 2002 Kelvin Aitken.
All rights reserved. Students may use this information for
personal research only. Not for commercial use.
Probably the most well known of the eight species of Horn
Shark is the Port Jackson Shark (Heterodontus portusjacksoni),
named after a bay in eastern Australia. Port Jackson Sharks
are one of the most common sharks seen in southern Australian
waters, especially in New South Wales. This species ranges
from southern Queensland around the southern States to Geraldton
in Western Australia. Port Jacksons have a distinctive bulky,
blunt head with a "pursed" mouth. They are usually
grey in colour with tints of brown or green, and a black-banded
pattern on the body similar in shape to the harness worn by
a seeing-eye dog.
Female Port Jackson sharks may travel as far as 850 km to
lay their eggs among shallow rocky reefs during late winter
and spring. These spiral-shaped eggs are a dark green or brown
when new but soon become almost black and are usually encrusted
with spots of algae. Females are supposed to push their eggs
into crevices but they are wedged in by wave action. Eggs
that have been left in the open or torn loose by storms are
often found washed ashore. The young pups that hatch 10–12
months later are about 15–20 cm long at first but they
grow to 1.5 m or more.
Divers and snorkelers may come across Port Jackson Sharks,
sometimes in groups of 10–20, lying in sheltered caves
or gullies on shallow rocky reefs during the day. Here they
sleep or rest until the night when they disperse to feed on
sea urchins and shells. Their scientific name, Heterodontus,
means 'different teeth' and refers to their spiky front teeth,
which are ideal for prying and holding; the fused teeth-plates
at the rear are perfectly developed for crushing shelled molluscs.
Crested Horn Sharks (Heterodontus galeatus) are only found
on the east coast of Australia in a confined region from southern
Queensland to Montague Island. Similarities with the Port
Jackson are their teeth, diet and body shape. They can be
best distinguished from the Port Jackson shark by the larger
crests above the eye and the lack of a harness-shaped pattern
on the body, having two indistinct dark bands or 'saddles'
over a yellowish brown base colour instead. They also have
rounder dorsal fins and do not congregate in groups.
Reproductive behaviour is very different from that of the
Port Jackson Shark. Females lay spiral-shaped egg cases with
long sticky tendrils up to 2 m long. The female chooses a
section of reef, often where other females have already deposited
their eggs, and tightly circle a suitable vertical projection,
such as sea tulips, kelp or a rock. As she rubs her body against
the reef the sticky tendrils, which have emerged slightly
from her body, become attached, pulling out the egg cases
as she swims away. The eggs are anchored to the reef by the
well-tangled tendrils. Eight months later the 20–22 cm
young emerge to grow to their adult size of 1.5 m
The Zebra Horn Shark (Heterodontus zebra) is found in the
Indo-Pacific being more common in Asian seas. Their name comes
from the striking pattern of dark vertical stripes on a pale
background.
Other species of Horn Shark include the Californian Horn
Shark (Heterodontus californicus) and the Mexican Horn Shark
(Heterodontus mexicanus)
Horn sharks can be sent into a state of trance-like ecstasy
by gently scratching their bellies and throats. However these
docile sharks should not be handled as their robust dorsal
spines can inflict a painful wound and their crushing teeth
can mash a wayward finger.
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